Low Cost Clay/Ceramic Steam Engine

[RulerOfSometh]

I am trying to design a low cost solar/steam engine for deployment where clean water and electricity are scarce. The prototyping I am currently doing is being done using plywood and a CNC router (mainly because that is what I have at my disposal). This will almost certainty not work as an end product (wood+steam+time is not a good combination… plus the lack of CNC routers in rural Africa). Ideally I would like to use minimally processed ground clay, as this would mean that much of the design could be made with local materials. While in Zambia with the U.S. Peace Corps, I designed a number of biomass gasification cookstoves out of clay as clay can be molded into almost any form, is free and withstands heat. What I'm a little unsure of is whether and/or how clay can be made to work in a moving system with a bit of friction and withstand relatively high pressures without using expensive machinery or materials. As the fundamentals of ceramics have been around for millennia (ex., pottery) it seems like it should be possible. Is there any easy way to make, albeit impure, Silicon nitride using sand, air and heat and can it be molded? I do not have a background in material science, ceramics or pottery so I'm seeking help from those who do.

 

[WhoWee]

Sometimes it helps to look at proven designs - even if very sophisticated compared to your own project.
http://ec.europa.eu/research/energy/pdf/stpp_solair_en.pdf

 

[Astronuc]

I am trying to design a low cost solar/steam engine for deployment where clean water and electricity are scarce. The prototyping I am currently doing is being done using plywood and a CNC router (mainly because that is what I have at my disposal). This will almost certainty not work as an end product (wood+steam+time is not a good combination… plus the lack of CNC routers in rural Africa). Ideally I would like to use minimally processed ground clay, as this would mean that much of the design could be made with local materials. While in Zambia with the U.S. Peace Corps, I designed a number of biomass gasification cookstoves out of clay as clay can be molded into almost any form, is free and withstands heat. What I'm a little unsure of is whether and/or how clay can be made to work in a moving system with a bit of friction and withstand relatively high pressures without using expensive machinery or materials. As the fundamentals of ceramics have been around for millennia (ex., pottery) it seems like it should be possible. Is there any easy way to make, albeit impure, Silicon nitride using sand, air and heat and can it be molded? I do not have a background in material science, ceramics or pottery so I'm seeking help from those who do.

Clay would have to be glazed to protect the porous structure. Silicon nitride is an engineered ceramic used in high temperature applications, but it requires purity and good control.

Metal is preferable for pressure-bearing pipes and vessels, and the type depends on the pressure, which will in part depend on temperature and flow rate.

The easiest system would be an evaporator in which solar energy is focussed (parabolic mirror, or collection of flat mirrors) on a mass (basin) of water which evaporates and then is collected on a (water-cooled) condenser. The amount of water collected will depend on the amount of energy input.

A more complicated system requires a pressure vessel containing water and on which the sun light it focussed through a batter of heliostats similar to the example cited by WhoWee.

Metals have to be corrosion resistant and the composition depends on the water chemistry. Stainless steel 304 would be appropriate, or 316 if the water is mildly saline, or 6Mo stainless steel if seawater is used.

 

[RulerOfSometh]

The prototype I'm working on right now uses focused sun light like you were suggesting and a scroll engine to harness the pressure caused by heating the water. What I'm trying to find is a method of having the moving parts be able to be made using local materials. The predominant available local materials in rural Sub-Saharan Africa (Zambia in particular) are wood and other organic material, clay, sand, loam, water, rocks and to some extent plastic bags/bottles/other trash. With these to go by, clay and sand seem to be the most malleable and easy to work with so that is what I am focusing on. Do you know whether there are glazes or methods of firing clay that make it able to withstand some force and friction? Do you have another suggestion?
Thanks.